Light-valve projection apparatus



June 16, 1942. p, J, HERES-r LIGHT-VALVE PROJECTION APPARATUS TORTELEVISION SIGNAL EEPRoDucING sYsTEMs original Filed April 29, 193eATTORNEY Reissued June 16, 1942 LIGHT-VALVE PROJECTION APPARATUS FORTELEVISION SIGNAL-REPRODUCING SYSTEMS Philip J. Herbst, Fort Wayne,Ind., assigner to Hazeltine Corporation, a corporation of Dela- WareOriginal No. 2,169,838, dated August 15, 1939, Serial No. 204,959, April29, 1938. Application for reissue May 2, 1941, Serial No. 391,571

16 Claims.

This invention relates to television signalreproducing systems andparticularly to new and improved light-valve projection apparatus usefulin such systems. The invention is especially directed to the provisionof an improved lightvalve projection apparatus of the scanning-ray tubetype whereby the transmission of light from an independent source may becontrolled by the scanning ray to reconstruct a transmitted image with ahigher intensity of illumination than is generally attainable inscanning-ray tubes.

This type cf light control is generally referred to in the art aselectrical transparency control. It has heretofore been proposed toemploy such a control in connection with signal-reproducing tubes oftelevision systems for the purpose of reconstructing an imagesuiiiciently bright to permit of its being projected in an enlarged sizeon a screen spaced from the tube. In general,

systems previously proposed to provide control of this type have beensubject to various objections including instability and the fact thatthey involve impractical or complicated apparatus.

It is an object of the present invention, therefore, to provide animproved light-valve projection apparatus of the scanning-ray tube typefor use in a television signal-reproducing system whereby a practicalelectrical transparency control may be obtained.

ln accordance with the invention, a television signal-reproducing systemincludes a light-valve projection apparatus comprising masking meansincluding a plurality of interspersed elementary transparent and opaqueareas, and lens means adapted normally to direct light from a sourcesubstantially-only onto said opaque areas of the masking means, wherebythe opaque areas normally intercept substantially all o! the lightdirected onto the masking means by the lens means. The projectionapparatus includes television signal-responsive means for varying thefocal lengths of incremental areas of the lens means, whereby themasking means transmits light from the source in accordance with thetelevision signal.

In accordance with one form of the invention, a light-valve projectionapparatus of the type described comprises masking means of transparentmaterial and the opaque areas thereof comprising a photonegative surfacedetermined by the lens means, whereby it normally interceptssubstantially all of the light from the source.

In accordance with a preferred form of the invention, a light-valveprojection apparatus of the type described is in the form of a target(Cl. TIS-7.5)

comprising a multiple lens system including a plurality of juxtaposedlens elements. A mask or screen is disposed adjacent the lens system andthe lens elements are adapted individually to focus light rays from agiven source onto restricted areas of the screen. Each of the lenselements has the property of varying its focus with respect to thescreen in response to excitation by a scanning ray. When the target isscanned by a ray, therefore, the foci of the successive lens elementsare varied so as to permit the light rays from the independent source topass through the screen adjacent their respective opaque areas.

In accordance with one approved embodiment of the invention, the targetcomprises a transparent plate having one of its surfaces formed toprovide a plurality of convex juxtaposed incremental areas which serveas the lens elements. The focal lengths of these elements aresubstantially equal to the thickness of the plate so that the lenselements are adapted normally to focus the light rays from the source onindividual areas at the opposite surface of the plate. The screen ispreferably formed as a film of photographic emulsion disposed over thefocal surface of the plate. The screen, while generally transparent, isdeveloped and fixed, after exposure to light from the source focusedthereon by the lens elements, so as to vprovide the opaque portions overthe individual focal areas of the lens system and, therefore, to benormally substantially completely opaque to light from such source.

For a better understanding of the invention, together with other andfurther objects, reference is had to the following description taken inconnection with the accompanying drawing, and its scope will be pointedout in the appended claims.

In the accompanying drawing, Fig. l is a schematic diagram of a portionof a television receiver embodying the present invention; Figs. 2, 3,and 4 are fragmentary plan views of portions of the light-valveprojection or target structure of the present invention, Fig. 2 showingthe lens system separately, Fig. 3 the screen separately afterdevelopment, and Fig. 4 the lens system with the mask or screen appliedthereto; while Fig. 5 is a diagrammatic fragmentary end view of aportion of the light-valve projection or target structure.

Referring now more particularly to Fig. l, the portion of the televisionreceiver there illustrated 55 includes a light-valve projectionapparatus applied to a cathode-ray signal-reproducing tube I andline-frequency and field-frequency generators and |2 having their outputcircuits connected to scanning coils I3 and Il, respectively. Thecathode-ray signal-reproducing tube I. includes the usual electron guncomprising a cathode I5 having a heater element Il, a control grid l1,an accelerating anode or screen Il, a focusing anode Il, and a secondanode 2li, which generally comprises a conductive coating on theinterior surface of the envelope. 'Ihe electron gun serves to develop,accelerate, and focus a beam of electrons or cathode rays, indicated atC, toward a target 2| which comprises a lightvalve projection apparatusand which embodies the present invention and will be hereinafterdescribed in detail.

Proper operating potentials are applied to the various electrodes of acathode-ray tube from a suitable source, for example, a voltage divider22 connected across a source of unidirectional voltage as indicated, byway of connections to the various electrodes from suitable points on thevoltage divider. A connection 23 is provided for applying thevideo-frequency modulation voltages to be reproduced to the control gridI1 by way of a suitable leak resistor 2l.

In conventional cathode-ray signal-reproducing tubes, the target 2|usually comprises a iluorescent screen which becomes luminous whenexcited by the cathode ray during the scanning operation. 'Ihe operationof the system just described, assuming for the moment that aconventional iiuorescent screen is employed as the target, is wellunderstood in the art and a detailed explanation thereof is unnecessary.Briefly, however, a cathode ray is developed, accelerated, and focusedby the electron gun toward the target in the well-known manner.Deilecting currents developed by generators Il and I2 are applied to thescanning coils I3 and il to provide magnetic fields to deflect thecathode rays horizontally and vertically, thereby to scan successiveilelds of horizontal parallel lines on the target. During this scanningaction, the intensity of the ray is varied in accordance with thevideofrequency modulation voltage applied to the control grid Il,corresponding to diiferent values of light and shade in the successiveelements of images being transmitted, so that the images arereconstructed on the fluorescent screen by s`uccessive spots of light ofvarying intensity. While a fluorescent screen cathode-ray tube, such asiust referred to, has proven generally satisfactory, the size of thetube necessarily limits the size of the picture that can be reproducedthereon. Moreover, such a uorescent screen ordinarily does not provide asufficiently intense light to permit projection of the reconstructedpicture and enlargement thereof on a separate screen.

In accordance` with the present invention, therefore, the improvedtarget or light-valve projection apparatus 2| is provided whereby apractical electrical transparency control is obtained. To this end, asource of illumination, as indicated by the lamp 25, is disposedadjacent the transparent end of the tube I! opposite the target 2|. Asuitable source 2G of filament voltage supply is provided for the lamp25, while a reflector 2l and condenser lens 2B may be disposed adjacentthereto to concentrate the light from the lamp and focus it in parallelrays on the inner surface of the target. Adjacent the opposite end ofthe tube a projecting lens system i9 is preferably disposed,

so that light images reconstructed by the light-valve projectionapparatus, as presently to be described, may be projected on a screen(not shown) to provide an enlarged reproduction of the image.

Referring now more particularly to the target 2|, its construction andoperation may best be explained with reference to Figs. 2-5, inclusive.Preferably, the target comprises a transparent plate III having one ofits surfaces formed to provide a multiplicity of separate minute convexjuxtaposed lens elements 3|. A portion of the plate and its lenselements alone are shown in Fig. 2. 'I'he lens elements are so shaped asto have local `lengths substantially equal to the thickness of platelll, so that normally they focus parallel light rays received from thesource 2l by way of the lens system 28 on restricted areas at theopposite surface of the plate III. A mask or screen 32. a portion ofwhich is shown separately in Fig. 3, is disposed over the outer surfaceof the plate ll. The screen is generally transparent but is opaque, asindicated at 32a, over the individual areas on which the light rays arenormally focused by the lens system. Thus, the screen or mask comprisesa plurality of interspersed elementary transparent and opaque areas, InFig. 4 the portion of the plate shown in Fig. 2 is shown superimposed onthe corresponding screen portion shown in Fig. 3. Preferably, the opaqueportions oi' the screen are determined by, and complementary to, thelens system itself and, in accordance with the preferred embodiment ofthe invention, this is accomplished by the particular manner in whichthe screen is constructed.

Referring more particularly to the construction of the target, the plate30 and its lens elements may, for example, be formed by disposing alayer of spherical transparent elements of quartz or other suitablematerial over a sheet of transparent material, such as glass. Thisstructure may be then heated to incipient fusion and the sphericalelements pressed into the glass sheet so as to form a substantiallyintegral structure. The cathode-ray tube may then be assembled with theplate-like lens structure forming one end thereof as shown in Fig. l. Asthe iinal step in the tube construction, a suitable coating ofphotographic emulsion may be applied to the outer surface of the plate30. The emulsion may thereupon be exposed to rays of light from thesource 25, focused thereon through the lens system 28, and subsequentlythe emulsion may be developed and fixed, thereby to provide the screen32 constituting a photonegative surface which is generally transparentbut includes opaque areas complementary or corresponding and determinedby, the lens system itself, thereby avoiding the leakage of lightthrough the screen that would result from any failure of the focal areasof the lens system to register with the opaque areas which mightotherwise result due to the minute size of the lens elements Il.

The substance of the lens elements is such as to give them the propertyof varying their focus with respect to the screen in response toexcitation by a scanning ra thereby to permit the light rays to passthrough the screen adjacent their respective opaque areas. Moreparticularly, changes in temperature or the well-known piezo-electriceil'ect caused by the impingement of a scanning beam. such as a cathoderay, on the lens elements, eil'ect variations either in the physicalconfiguration of the lens eements or in their indices of refraction, orboth.

The lens elements 3| comprise a cathode-ray sensitive element of thelens system and may be of any suitable material, such as quartz in thecrystalline stage, which exhibits sensitivity to electron bombardment,both as to changes in its dimensions and its index of refraction andwhich is also quite satisfactory for the purpose of sealing in vacuum.Also certain salts, such as Rochelle salts, may be used. The latter,while more sensitive to electron bombardment than quartz, is not,however, as adaptable for use in high vacuum apparatus, which musigenerally be exhausted at high temperatures. The individual lcnselements may be formed by grinding small crystals in a continuouslyrotating mill, until they assume the required spherical form.

In Fig. 5 a portion of the target is shown with parallel light rays,indicated by the broken lines, passing through its lens elements. Undernormal conditions, the rays are focused by the lens elements 3| on theopaque portions 32a of the screen, as shown, whereby the opaque areas32a intercept substantially all of the light directed on the maskingmeans by the lens system. A cathode ray, however, indicated at C, isshown impinging upon one of the lens elements and varying its focus, asdescribed above, so that the defocused light rays pass through thescreen at the portions adjacent the opaque portions corresponding tothis particular lens element.

In the operation of the receiving apparatus embodying the presentinvention which is shown in Fig. 1, the light rays from the source areprojected by means of the lens system 2B in parallel rays on the innersurface of the target ZI. Due| to the focusing of the rays by theelcments 3| and the complementary opaque por tions of the screen 32,however, no light normally passes through the mask or screen 32.

However, as the television signal-modulatedelectron beam C is deflectedto scan a series of parallel lines or fields on the target, itsuccessively impinges upon the lens elements 3| and effects a variationin their foci, thereby successively varying the focal lengths ofincremental areas of the lens system to an extent corresponding to theintensity of the electron beam as controlled by the video-modulationsignal applied to the control grid of the tube. This defocusing actionthus permits the light rays to pass through the areas of the screenadjacent the opaque portions corresponding to the particular lenselements on which the beam is focused, the

amount of the light transmitted. through each incremental area beingdependent upon the amount of defocusing of the lens elements included insuch area and thus on the 'intensity of the cathode-ray beam. Thus, themask or screen 32 transmits light from the source 25 in accordance withthe television signal. The transmitted image is thus apparentlyreconstructed on the outer surface of the target. Moreover, thebrightness of this image is suiciently intense to permit its beingprojected by the lens system 29 upon a suitable screen spaced from thetarget, thereby to provide an enlarged image. The size of the lenselements will be substantially smaller than the size of the cathode-rayspot, preferably having a diameter of the order of one-tenth thediameter of the spot to ensure uniformity of the lens action.

While there has been described what is at present considered to be thepreferred embodiment of this invention, lt will be obvious to thoseskilled in the art that various changes and modifcations may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

l. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a multiple lens system including a plurality ofjuxtaposed lens elements, a screen adjacent said lens system, said lenselements being proportioned to focus parallel light rays on individualseparate areas of said screen, said screen being generally transparentbut opaque over said areas, each of said lens elements having theproperty of varying its focus with respect to said screen in response toexcitation by a scanning ray, thereby to permit said light rays to passthrough said screen adjacent its respective opaque areas.

2. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a multiple lens system including a plurality ofjuxtaposed lens elements, a screen adjacent said lens system, said lenselements being adapted to focus parallel light rays on said screen, saidscreen being generally transparent but having opaque areas determinedby, and complementary to, said lens system, whereby said target isnormally opaque to said light rays, each of said lens elements havingthe property of varying its focus with respect to said screen inresponse to excitation by a scanning ray, thereby to permit said lightrays to pass through said screen adjacent its respective opaque areas.

3. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a transparent plate having formed on one of itssurfaces a plurality of convex juxtaposed incremental areas comprisingseparate lens elements having focal lengths substantially equal to thethickness of said plate, whereby said lens system is adapted to focusparallel light rays on individual areas at the opposite surface of saidplate, a screen disposed over said opposite surface, said screen beinggenerally transparent but opaque at portions corresponding to said focalareas, each of said lens elements having the property of varying itsfocus with respect to said opposite surface in response to excitation bya scanning ray, thereby to permit light rays to pass through said screenadjacent its respective opaque areas.

4. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a transparent plate having formed on one surfacethereof a multiple lens system including a plurality of juxtaposed lenselements, a screen comprising a lm of photographic emulsion disposed onthe opposite surface of said plate, said lens system being proportionedto focus parallel light rays on individual areas at the opposite surfaceof said plate, said screen being generally transparent but developed andfixed after exposure to light rays focused thereon by said lens elementsto render said areas opaque, each of said lens elerr ents having theproperty of varying its focus with respect to said screen in response toexcitation by a scanning ray, thereby t0 permit said light to passthrough said screen adjacent its rerpective opaque areas.

5. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a transparent plate having formed on one of itssurfaces a plurality of convex juxtaposed incremental areas providingseparate lens elements having focal lengths substantially equal to thethickness of said plate, whereby said lens elements are adapted to focusparallel light rays on individual areas at the opposite surface of saidplate, a screen comprising a nlm of a photographic emulsion disposedover saidopposite surrace, said screen being generally transparent butdeveloped and iixed after exposure to said light rays focused thereon bysaid lens elements to render said areas opaque, each of said lenselements having the property oi varying its focus with respect to saidscreen in response to excitation by a scanning ray, thereby to permitsaid light rays to pass through said screen adjacent its respectiveopaque areas,

6. In a television signal-reproducing system, a light-valve projectionapparatus comprising, masking means including a plurality ofinterspersed elementary transparent and opaque areas, lens meansincluding only substantially rigid lens elements and adapted normally todirect light from a source substantially only onto said opaque areas ofsaid masking means, whereby said opaque areas normally interceptsubstantially all of the light directed onto said masking means by saidlens means, and television signalresponsive means for varying the focallengths of incremental areas of said lens means, whereby said maskingmeans transmits light from said source in accordance with saidtelevision signal.

"I. In a television signal-reproducing system, a light-valve projectionapparatus comprising, masking means including a plurality ofinterspersed elementary transparent and opaque areas, lens meansincluding a. cathode-ray sensitive element and adapted to direct lightfrom a source substantially only onto said opaque areas of said maskingmeans, whereby said opaque areas normally intercept substantially all ofthe light directed onto said masking means by said lens means, andtelevision signal-responsive cathode-ray means for scanning said lenselement in a predetermined pattern successively to vary the focallengths of incremental areas of said lens means, whereby said maskingmeans transmits light from said source in accordance with saidtelevision signal.

8. In a television signal-reproducing system, a light-valve projectionapparatus comprising, masking means including a plurality ofinterspersed elementary transparent and opaque areas, lens means adaptednormally to direct light from a source onto restricted areas of saidmasking means, said masking means being of transparent material and saidopaque areas thereof comprising a photonegative surface dete N ed bysaid lens means, whereby it normally intero ts substantially all of thelight from said source, and television signal-responsive means forvarying the focal lengths of incremental areas of said lens means,`whereby said masking means transmits light from said source inaccordance with said television signal. Y

9. In a television signal-reproducing system, a light-valve projectionapparatus comprising, masking means including a plurality ofinterspersed elementary transparent and opaque areas, lens meansincluding an element of transparent material adapted normally-to directlight from a source onto restricted areas of said masking means, saidmasking means being oi' transparent material and said opaque areasthereof comprising a photonegative surface determined by said lensmeans, whereby it normally intercepts substantially all oi the lightfrom said source. and television signal-responsive means tor varying theindex of refraction of incremental areas of said transparent material tovary the focal lengths of incremental areas of said lens means, wherebysaid masking means transmits light from said source in accordance withsaid television signal.

10. In a television signal-reproducing system, a light-valve projection.apparatus comprising, lens means including a substantially rigid lenselement adapted to have a light-transmission characteristic of elementalareas thereof modified in response to excitation by a scanning ray,masking means arranged in cooperative relation with said lens meansnormally to mask a substantial part of the light transmitted thereto bysaid lens means from a light source, and television signal-responsivescanning-ray means for modifying said light-transmission characteristicof elemental areas of said lens means to permit an increased amount oflight from said source to pass said masking means.

l1. In a television signal-reproducing system. a light-valve projectionapparatus comprising, lens means adapted to have the index of refractionof elemental areas thereof modiiied in response to excitation by ascanning ray, masking means arranged in cooperative relation with saidlens means normally to mask a substantial part of the light transmittedthereto by said lens means from a light source, and televisionsignalresponsive scanning-ray means for modifying the index ofrefraction of elemental areas of said lens means, to permit anincreasing amount oi light from said source to pass said masking means.

12. In a television signal-reproducing system, a light-valve projectionapparatus comprising, lens means including a plurality of lens elementsone of which comprises effectively a mosaic of elemental substantiallyrigid lenses, masking means arranged in cooperative relation with saidlens means normally to mask a substantial part of the light projectedthereto by said lens means from a light source, and televisionsignal-responsive means for modifying a light-transmissioncharacteristic of incremental areas of said one element to permit anincreasing amount of light from said source to pass said masking meansin accordance with said television signal.

13. In a television signal-reproducing system, a light-valve projectionapparatus comprising, lens means including a plurality of lens elementsone of which comprises effectively a plurality of juxtaposed elementalsubstantially rigid lenses, masking means arranged in cooperativerelation with said lens means normally to mask a substantial part oi'the light projected thereto by said lens means trom a light source, andtelevision signal-responsive means for modifying a lighttransmissioncharacteristic of incremental areas of said one element to permit anincreasing amount of light from said source to pass said masking meansin accordance with said television signal.

14. In a television signal-reproducing system, a light-valve projectionapparatus comprising, masking means including a plurality ofinterspersed elementary transparent and opaque areas, lens meansincluding only substantially rigid lens elements and adapted normally tofocus light from a source substantially only onto said opaque areas ofsaid masking means, whereby said opaque areas normally interceptsubstantially all of the light directed onto said masking means by saidlens means, and television signalresponsive means for varying the focallengths of incremental areas of said lens means, whereby said maskingmeans transmits light from said source in accordance with saidtelevision signal.

l5. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a light source, a viewing means, masking meanshaving a plurality of interspersed elementary transparent and opaqueareas and interposed in the optical path between said source and saidviewing means, lens means including only substantially rigid lenselements and adapted normally to focus substantially all of the lightfrom said source onto said opaque areas of said masking means, means forell'ectively altering the optical path-length of elementary portions ofthe optical path through said lens means for varying the amount of lightmasked from said viewing means by said opaque areas of said maskingmeans, and means for controlling said lastnamed means in accordance withsaid television signal to form on said viewing means a visible imagecorresponding to said television signal.

16. In a television signal-reproducing system, a light-valve projectionapparatus comprising, a transparent plate having formed on one surfacethereof a multiple lens system including aplurality of juxtaposed lenselements, said lens elements being proportioned to focus parallel lightrays on individual areas at the opposite surface cf said plate, a screendisposed adjacent said opposite surface of said plate, said screen beinggenerally transparent but opaque at said individual areas and being alsoopaque over all areas corresponding to the areas of said transparentplate not covered by said lens elements, each of said lens elementshaving the property of varying its focus with respect to said screen inresponse to excitation by a scanning ray, thereby to permit said lightto pass through said screen adjacent its respective opaque areas.

PHILIP J. HERBST.

